This invention relates to a parabolic signal generator used with the deflection circuit and dynamic focusing circuit (will be termed "DAF" hereinafter) of television receivers and display apparatus.
In order to improve the focus characteristics of the cathode ray tube (will be termed "CRT" hereinafter) used in recent television receivers and display apparatus having large screens, DAF circuits are introduced so as to improve the peripheral focus characteristics of the CRT. This purpose is achieved by operating the DAF circuit to generate a parabolic waveform and applying the waveform to the focus terminal of the CRT.
The following explains a conventional parabolic signal generator. FIG. 2 shows the conventional parabolic signal generator. In FIG. 2, symbol 1 denotes a saw-tooth wave generation circuit, 3 is an absolute value circuit, 5, 7, 10, 14, 17 and 24 are resistors, and 6, 8, 9, 11, 12, 13, 15 and 16 are diodes.
The operation of the foregoing conventional circuit arrangement will be explained. The saw-tooth wave generation circuit 1 converts a current flowing in the deflection coil into a voltage shown in FIG. 3A, the absolute value circuit 3 folds the saw-tooth waveform with respect to its center to produce a waveform shown in FIG. 3B, and a polygonal approximation circuit formed of the resistors 5, 7, 10, 14, 17 and 24 and the diodes 6, 8, 9, 11, 12, 13, 15 and 16 operates to make parallel connections of registers in response to the conduction of sets of diodes which are in serial connection with the respective resistors, so that a parabolic waveform is produced.